1. Field of the Invention
The present invention relates to an exposure apparatus and a correction apparatus.
2. Description of the Related Art
A projection exposure apparatus configured to illuminate an original (e.g., a reticle or a mask) by an illumination optical system, and expose a pattern of the original on a substrate such as a wafer by using a projection optical system has been conventionally used. There is an increasing demand to improve resolution and throughput of such exposure apparatuses. One efficient method to obtain high resolution is to shorten a wavelength of an exposure light and increase a numerical aperture (“NA”) of the projection optical system (also called “high-NA”).
If an excimer laser of larger size replaces an extra high pressure mercury lamp of relatively smaller size in order to shorten a wavelength of an exposure light, an exposure apparatus as a main body cannot be equipped with a light source. For example, the main exposure apparatus has to be arranged on the second floor, and the light source unit has to be on the first floor. As a result, an oscillation displaces the relative position between the main exposure apparatus and the light source unit, causing the positional and the angular misalignment of the optical axes (a central beam of light) of the illumination light and the illumination optical system. Accordingly, the positional and the angular misalignment needs to be eliminated as disclosed in Japanese Patent Laid-Open No. 11(1999)-145033, Japanese Patent Laid-Open No. 2000-77315, and Japanese Patent Laid-Open No. 2005-150541.
Meanwhile, a contrast of an interference pattern formed by a line and space (L&S) pattern of an original to a photoresist will be lower when it is P-polarized light to diffraction light of the L&S, and in particular it will be remarkably lower along with a high NA such as immersion exposure. For this reason, polarized illumination which utilizes S-polarized light (i.g., light, of which the oscillation direction of the vector in the electric field is parallel to the base surface and is perpendicular to the light traveling direction) is considered to be applied. In this case, the imaging performance becomes sensitive to birefringence that is a polarization characteristic of an optical system.
Japanese Patent Laid-Open No. 11(1999)-145033 and Japanese Patent Laid-Open No. 2000-77315 propose that a positional misalignment of an optical axis is corrected by rotating a mirror, and a positional misalignment of an optical axis is corrected by tilting a parallel plate. However, birefringence that is so called “intrinsic birefringence” due to the crystal structures can occur by tilting the parallel plate. In particular, the parallel plate has a thickness of 50 to 150 mm and the tilting angle of around 20° to the optical axis. Then, the influence of the intrinsic birefringence cannot be ignored. Then, the influence of the intrinsic birefringence cannot be ignored. Sufficiently significant intrinsic birefringence will distort a polarization state in the polarized illumination from the predetermined state and lower the imaging performance. Further, the thick parallel plate having the low light transmittance will lower the throughputs.